Method for vacuum deposit on a curved substrate

ABSTRACT

The invention concerns a method which consists in a process known per se in producing, on the curved substrate ( 10 ) to be treated, a film of material derived from a specific material source ( 13 ). The invention is characterized in that it consists in inserting, between the curved substrate ( 10 ) and the material source ( 13 ), a mask ( 19 ) relative to the curved substrate ( 10 ), preferably selecting as mask ( 19 ), a mask comprising a ring-shaped part ( 20 ). The invention is particularly useful for providing lenses with antiglare treatment.

BACKGROUND OF THE INVENTION

The present invention relates in a general manner to the vacuumtreatment of any substrate of the kind in which, using a sputteringtechnique, the deposition of a layer of material coming from a givensource of material is carried out, everywhere, in a chamber, on thissubstrate by subjecting, for example, this source of material, whichthen serves as a cathode, to a suitable ion bombardment, the result ofwhich is that particles are torn off it and these are then deposited onthe substrate.

The invention is aimed more particularly at the case in which thetreated substrate is a curved substrate, or even a highly curvedsubstrate, as is the case, at least, in certain spectacle lenses,particularly those of high power.

The expression “curved substrate” should therefore be understood to meanhere, more generally, a substrate which, in the manner of a spectaclelens, has a curvature accentuated to a greater or lesser extent in atleast one transverse plane.

Thus, as is known, it is usual to apply a vacuum treatment to certainspectacle lenses in order to give them particular properties, forexample antireflection properties.

One of the problems to be solved in terms of material is to ensure thecomplete thickness uniformity desirable for the layer of material thusdeposited.

The term “thickness” should be understood to mean here, and throughoutthe following, the optical thickness of the deposited layer, that is tosay the physical thickness of this layer multiplied by the refractiveindex of the material of which it is composed.

Should good uniformity of this thickness be lacking, any possibleresidual reflection runs the risk of resulting in undesirableiridescence.

Now, the thickness of the deposited layer of material is inverselyproportional to the distance of the spectacle lens, or more generally ofthe treated substrate, from the corresponding source of material.

When, as is the case here, the substrate is curved, this distance isgreater at its periphery than its centre and the thickness of thecoating obtained is therefore smaller at this periphery than at itscentre.

This thickness difference may become significant when, for practicalreasons, the curved substrate is placed a short distance from the sourceof material, the difference in distance between its periphery and itscentre with respect to this source of material then becoming appreciablebecause of its very curvature.

In practice, this thickness difference may commonly be as much as 20%,depending on the substrates and the chamber employed.

SUMMARY OF THE INVENTION

The subject of the present invention is, in a general manner, anarrangement allowing this thickness difference to be reduced verysimply.

More specifically, the subject of the invention is firstly a process forthe vacuum treatment of any curved substrate, of the kind in which alayer of material coming from a given source of material is deposited onthis curved substrate, this process being generally characterized inthat a mask is interposed between the curved substrate and the source ofmaterial at a certain distance from the curved substrate, the said maskbeing stationary with respect to the curved substrate; the subject ofthe invention is also any mask suitable for implementing such a process.

Admittedly, it is already known to employ, for various reasons, a maskduring the vacuum treatment of a curved substrate, as is the case, forexample, in U.S. Pat. No. 5,225,057.

However, in this U.S. Pat. No. 5,225,057, the treated curved substrateis driven in rotation about itself, so that the mask is not stationarywith respect to it.

Furthermore, this mask is employed only for limiting the beam angle ofthe beam by means of which the desired deposition is carried out,without it being intended for there to be any effect on the actualthickness of the layer of material obtained in terms of this deposition.

Admittedly, it is also already known, especially from U.S. Pat. No.5,389,397, to use, during the vacuum treatment of a substrate, a maskwhich is stationary with respect to this substrate.

However, in this U.S. Pat. No. 5,389,397, the treated substrates areflat.

With regard to the deposition peculiarities involved when the substrateis a curved substrate, it was impossible to imagine a priori that astationary mask could also be suitable for such a curved substrate.

Furthermore, in this U.S. Pat. No. 5,389,397, the mask used is solid.

Now, somewhat surprisingly, it turns out that, with the mask accordingto the invention, significant results are obtained when this maskincludes an annular part.

Without there being any certainty in this regard, it is conceivable, forexample, that, at the working pressures employed, which are generallygreater than 0.1 Pa, since the mean free path of the coating particlesinvolved is of the order of a few millimeters, these coating particlesare subject to multiple reflections from the atoms of the plasma gas,that, because of these multiple reflections and because of theconfiguration of the chamber employed, a greater flux of particles isnormally created in the direction of the centre of the substrate than inthe direction of its periphery and that, with the interposition of amask according to the invention, and more particularly of a maskincluding an annular part, between the source of material and thesubstrate, this flux of particles is probably less directional, thisflux then being at least partially limited at the centre of thesubstrate, which is the point where, in the absence of such a mask, asurplus of deposited material is usually observed.

Nevertheless, it is observed, and this is borne out by tests, that, witha mask having, according to the invention, an annular part, the measuredthickness difference, for the coating obtained, between the periphery ofthe treated curved substrate and the centre of the latter, instead ofbeing of the order of 20%, may advantageously be reduced to less than15%, or even less than 10%, all other conditions being the same.

Even more satisfactory results may be observed when, in a development ofthe invention, the mask employed has, inside its annular part, at leastone crosspiece which connects two regions of this annular part together,for example along a diameter of the latter, with, optionally in thiscase, in a complementary development of the invention, on the outside ofthe annular part, at each of the ends of such a crosspiece, an arm whichextends radially with respect to the annular part in the extension ofthis crosspiece.

In such a case, the thickness difference observed between the peripheryof the treated curved substrate and the centre of the latter may,advantageously, be reduced to less than 5%, all other conditions beingthe same.

In all cases, the results obtained with a mask according to theinvention are all the more surprising since, in practice, this mask mayadvantageously have, with respect to the treated curved substrate, arelatively small extension, which, if desired, makes it possible tolimit the overall size of the assembly to that of the curved substratealone, and which thereby makes it possible, as a corollary, to avoidpossible shadowing difficulties.

In particular, especially favourable results may be obtained with a maskwhose projection on a plane in a direction perpendicular to this planehas an area of less than 10%, or even less than 5%, of the area of theprojection of the curved substrate on this same plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the invention will, moreover,emerge from the description which follows, given by way of example, withreference to the appended schematic drawings in which:

FIG. 1 is a perspective view of a curved substrate to be treated,illustrated in place on a substrate, with the mask with which it isassociated, according to the invention;

FIG. 2 is an axial sectional view of the assembly, on the line II—II inFIG. 1;

FIG. 3 is, taken from FIG. 1, but on a different scale, a perspectiveview of the mask according to the invention, illustrated in isolation;

FIG. 4 is, on a larger scale, a partial axial sectional view of thismask, on the line IV—IV in figure 3;

FIG. 5 is a partial perspective view, similar to that in FIG. 3, for analternative embodiment;

FIG. 6 is also a perspective view, similar to that in FIG. 3, foranother alternative embodiment;

FIG. 7 is, on a larger scale, a partial axial sectional view of thisother alternative embodiment, on the line VII—VII in FIG. 6; and

FIGS. 8, 9 and 10 are perspective views which, also being similar tothat in FIG. 3, each relate, respectively, to other alternativeembodiments of the mask according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

These figures illustrate, by way of example, the application of theinvention to the case in which the curved substrate 10 to be treated isa spectacle lens or, more specifically, a disc of circular contour fromwhich such a spectacle lens is subsequently cut out.

Let D₁ be the diameter of this curved substrate 10 along its contour.

This diameter D₁ is usually between 65 mm and 80 mm.

In the embodiment illustrated, the curved substrate 10 is, for example,concavo-convex.

When a vacuum treatment has to be applied to it, such a curved substrate10 is usually supported, around its periphery, by a support 11 suitablefor holding it.

Since this support 11 is well known per se and does not pertain at allto the present invention, it will not be described here.

Furthermore, it is also for the sake of convenience that it isillustrated in FIGS. 1 and 2 in the form of a flat disc of circularcontour.

In fact, this support 11 may have very diverse configurations, or indeedmay even be perforated.

Nevertheless, for the desired vacuum treatment, and in a manner knownper se, a layer of material coming from a suitable source of material 13is deposited on the curved substrate 10 thus supported by a support 11,in a chamber 12 shown schematically by the broken lines in FIG. 2, thesource of material also being shown schematically in broken lines inthis FIG. 2.

A machine used, for example, for this purpose is sold by Applied VisionLtd under the brand name PLASMACOAT AR.10™.

This machine is also described in International Patent Application No.WO-A-92/13114.

For example, and as shown schematically at 14 in FIG. 2, the source ofmaterial 13 is placed at a negative potential, in order to form acathode, and introduced into the chamber 12 are, on the one hand, forexample via a nozzle 15, an inert gas, for example argon, and, on theother hand, for example via a nozzle 16, an active gas, for exampleoxygen.

In general, a gas pressure of greater than 0.1 Pa is used.

Preferably, this gas pressure is between 0.2 Pa and 2 Pa.

As a corollary, the support 11 is usually, and as illustrated, anindividual support and, together with other supports 11 of the sametype, each supporting a curved substrate 10 to be treated, it is fitted,as shown schematically by broken lines in FIG. 2, onto a collectivesupport 18, for example in the form of a plate, mounted so as to rotatein the chamber 12.

As a variant, the support 11 may just as well move in a linear fashionbeneath the source of material 13.

Whatever the case, the inert gas introduced via the nozzle 15 ionizes onentering the chamber 12, forming as it were a plasma therein, and thepositive ions which thus arise therefrom bombard the source of material13, which forms a target, and they thus tear off from this source ofmaterial 13 particles which, while combining with the active gasintroduced via the nozzle 16, become deposited on the curved substrate10, forming on its surface the desired layer of material.

The above arrangements are well known per se and will therefore not bedescribed in detail here.

According to the invention, a mask 19 is interposed between the curvedsubstrate 10 and the source of material 13, this mask being stationarywith respect to the curved substrate 10.

Preferably, and as illustrated, a mask having an annular part 20 ischosen as the mask 19.

In practice, this annular part 20 has a circular contour.

For example, and as illustrated, a mask whose annular part 20 has, onthe outside, a diameter D₂ of less than twice the diameter D₁ of thecurved substrate 10 is chosen for the mask 19.

More specifically, a mask whose annular part 20 has, on the outside, adiameter D₂ of between one quarter of the diameter D₁ of the curvedsubstrate 10 and twice this diameter D₁ is preferably chosen for themask 19.

Moreover, it is possible to indicate, in this regard, by way ofnumerical example, but without this being able to result in anylimitation of the invention, that, with a curved substrate 10 whosediameter D₁ is about 65 mm, whose power is six dioptres and whose radiusof the convex front face is 62.13 mm, satisfactory results have beenobtained with a mask 19 whose annular part 20 has, on the outside, adiameter D₂ of between 20 mm and 130 mm.

Whatever the case, since the curved substrate 10 is supported, asindicated above, by a support 11, the mask 19 is fastened, for example,to this support 11.

In the embodiment illustrated, the mask 19 is, in practice, attached tothe support 11 by a bracket 22 and extends in cantilever fashion fromthe end of the cross-arm 23 of this bracket 22.

Of course, it is preferred to make this bracket 22 as small as possibleso as to minimize the shadowing that it may cause during deposition ofmaterial on the curved substrate 10.

Nevertheless, and as illustrated, the mask 19 is preferably placed at adistance from the curved substrate 10 and approximately parallel to thelatter.

Let d be this distance, measured between the mask 19, at its base, andthe highest point of the curved substrate 10, as indicated in FIG. 2.

For example, this distance d is less than twice the diameter D₁ of thecurved substrate 10.

Preferably, it is between one tenth of the diameter D₁ of the curvedsubstrate 10 and half this diameter D₁.

Moreover, it is possible to indicate in this regard, by way ofnon-limiting example, and under the same conditions as above, thatsatisfactory results have been obtained with a distance d between themask 19 and the curved substrate 10 of less than 130 mm and preferablybetween 7 mm and 30 mm.

In the embodiments illustrated in FIGS. 1 to 5, the mask 19 is reducedto its annular part 20.

For example, and as illustrated, the cross section of this annular part20 is generally rectangular.

Let H be its height, measured along the axis of the curved substrate 10,and therefore perpendicular to the support 11 which supports it, and letE be its radial thickness, measured parallel to this support 11.

Preferably, and this is the case in the embodiments illustrated, theannular part 20 of the mask 19 has, in cross section, a height H greaterthan its radial thickness E.

For example, this height H is less than 15 mm.

Preferably, it is between 1 mm and 15 mm.

Moreover, it is possible to indicate in this regard, by way ofnon-limiting example, and under the same conditions as above, thatsatisfactory results have been obtained with a height H of between 1 mmand 10 mm.

Likewise, satisfactory results have been obtained with a radialthickness E of less than 2 mm.

For example, this radial thickness E is less than 1 mm.

Moreover, it is possible to indicate in this regard, by way ofnon-limiting example, and under the same conditions as above, thatsatisfactory results have been obtained with a radial thickness E ofabout 0.1 mm.

Moreover it appears that, in order to obtain satisfactory results, it isdesirable to take into account the diameter D₁ of the curved substrate10 to be treated when choosing the diameter D₂ of the annular part 20 ofthe mask 19 employed.

To do this, according to the invention, care is taken to ensure that atleast one of the following formulae, and preferably each of them, issatisfied:

$\begin{matrix}{{d + H} = {A \cdot \frac{D_{2}}{2}}} & (I) \\{d = {B \cdot \frac{D_{2}}{2}}} & ({II})\end{matrix}$D₁=C.D₂  (III)in which d, H, D₁ and D₂ are the parameters already mentioned above, inwhich:

A is a coefficient of between 0.8 and 1, being for example about 0.92;

B is a coefficient of between 0.7 and 0.9, being for example about 0.77;

and C is a coefficient of between 2 and 3, being for example about 2.5.

In the embodiment illustrated in FIG. 5, the height H has a value twicethe value that it has in the embodiment illustrated in FIG. 3.

In the embodiments illustrated in FIGS. 6 to 10, the mask 19 includes,inside its annular part 20, at least one crosspiece 24 which linkstogether two regions of this annular part 20.

For example, and as illustrated in FIGS. 6 to 8, a single crosspiece 24is provided and this crosspiece 24 extends along a diameter of theannular part 20.

Furthermore, in these embodiments, the cross section of this crosspiece24 is generally rectangular and it extends approximately parallel tothat of the annular part 20.

In the embodiments illustrated in FIGS. 6 to 8, the crosspiece 24 hasitself, in cross section, a height H′ equal to the height H of theannular part 20 and a radial thickness E′ equal to the radial thicknessE of this annular part 20.

It therefore extends, level with the annular part 20, both on the sideof one of the portions of the latter and on the side of the other ofthese portions.

However, of course, the crosspiece 24 may, as a variant, have, in crosssection, a height H′ different from the height H of the annular part 20and/or a radial thickness E′ different from the radial thickness E ofthis annular part 20.

This is the case, by way of example, at least for the height H′, in theembodiments illustrated in FIGS. 9 and 10, in which, moreover, the mask19 according to the invention includes at least two crosspieces 24.

For example, and as illustrated, only two crosspieces 24 are thusprovided and they are perpendicular to each other, each extending inpractice along a diameter of the annular part 20.

For example, these two crosspieces 24 each have a construction similarto that of the previous cross section 24.

However, in the embodiments illustrated, their height H′ is equal tohalf the height H of the annular part 20.

For example, and as illustrated, they extend halfway up this annularpart 20.

Finally, in the embodiment illustrated in FIG. 10, the mask 19 includes,on the outside of its annular part 20, at least one arm 25 which extendsradially with respect to this annular part 20, in a cantilever fashionfrom the latter.

In practice, this arm 25 has a structure similar to that of thecrosspieces 24 and it extends along the extension of such a crosspiece24.

Also in practice there is an arm 25 at each of the ends of a crosspiece24 and, for both of the crosspieces 24, the various arms 25 thus usedhave the same length.

It is possible to indicate in this regard, by way of non-limitingexample, and under the same conditions as above, that satisfactoryresults have been obtained with arms 25 having a length L of 10 mm.

In FIG. 6, the height H of the annular part 20 of the mask 19 is equalto that of the embodiment in FIG. 3.

On the other hand, in FIGS. 8 to 10, this height H has a value equal tothat of the embodiment illustrated in FIG. 5.

However, in both cases this height H may be different.

Furthermore, according to an alternative embodiment (not illustrated),this height H of the annular part 20 of the mask 19 varies along theperimeter of the latter, extending, for example, between 2 mm and 15 mm,in order to take into account the relative movement between this mask 19and the source of material 13.

In all cases, simply because of the structure of the mask 19 accordingto the invention, the shadow cast by the latter on the treated curvedsubstrate 10 is advantageously particularly small.

More specifically, a mask whose projection on a plane in a directionperpendicular to this plane has an area of less than 10% of the area ofthe projection of the curved substrate 10 on this same plane under thesame conditions is chosen, in this regard, according to the invention,for the mask 19, the plane of projection thus taken into account being,for example, that of the support 11 on which the treated curvedsubstrate 10 rests.

Again, more specifically, a mask whose projection, under the conditionsindicated above, has an area of less than 5% of the area of theprojection of the curved substrate 10 is preferably chosen for the mask19 according to the invention.

In all cases too, and to the extent that this can be confirmed, thematerial of which the mask 19 according to the invention is composedseems to have no effect on the results obtained.

This material may therefore be various materials.

For example, it may just as well be paper as stainless steel.

The table below summarizes, figure by figure, the results obtained withthe various embodiments briefly described above.

In this table, Δ gives, in percent, the thickness difference observedfor the coating obtained during a given treatment between the peripheryof the curved substrate 10 and the centre of the latter.

D₁ D₂ H E mm mm mm mm Δ % FIGS. 3, 4 65 26 1 0.1 14 FIG. 5 65 26 2 0.112 FIGS. 6, 7 65 26 1 0.1 13 FIG. 8 65 26 2 0.1 7 FIG. 9 65 26 2 0.1 3.7FIG. 10 65 26 2 0.1 3.4

Of course, the present invention is not limited to the embodimentsdescribed and illustrated, but encompasses any alternative embodimentand/or implementation.

In particular, the contour of the annular part of the mask employed isnot necessarily circular.

For example, this contour could be elliptical.

It could even have a more complex shape, being, for example, in the formof a spiral.

Furthermore, it is possible to vary the pressure of the gases inside thechamber employed.

For example, by increasing this pressure, it is possible to reverse thethickness difference observed, the thickness of the coating obtainedthen being less at the centre of the treated curved substrate than atthe periphery of the latter.

1. Process for the vacuum treatment of any curved substrate having acircular contour with a given diameter (D₁), comprising the steps of:depositing a layer of material coming from a given source of material(13) on the curved substrate (10), while interposing a mask (19) betweenthe curved substrate (10) and the source of material (13) at a certaindistance from the curved substrate (10) and approximately parallel tothe curved substrate, the mask being stationary with respect to thecurved substrate (10), and selecting the mask to have an annular part(20) with a diameter (D₂) between one quarter and twice the givendiameter (D₁) of the curved substrate (10); wherein the certain distanceis at least one tenth of, but less than twice, the diameter (D₁). 2.Process according to claim 1, comprising the further step of selectingthe mask to have a projection on a plane, in a direction perpendicularto the plane, with an area of less than 10% of the area of theprojection of the curved substrate (10) on the plane.
 3. Processaccording to claim 2, comprising the further step of selecting the maskto have the projection with an area of less than 5% of the area of theprojection of the curved substrate (10).
 4. Process according to claim1, wherein the certain distance is less than half the diameter (D₁) ofthe curved substrate.
 5. Process according to claim 1, comprising thefurther steps of: supporting the curved substrate (10) by a support(11), and fastening the mask (19) to the support (11).
 6. Processaccording to claim 1, wherein a gas pressure of greater than 0.1 Pa isused in the depositing step.
 7. Process according to claim 1, comprisingthe further step of selecting the mask to have the annular part (20)have, in cross section, a height (H) greater than a radial thickness (E)of the annular part.
 8. Process according to claim 7, wherein the height(H) of the annular part (20) of the mask (19) is less than 15 mm. 9.Process according to claim 7, wherein the height (H) of the annular part(20) of the mask (19) varies along a perimeter of the annular part. 10.Process according to claim 7, wherein the mask consists of the annularpart (20).
 11. Process according to claim 7, wherein the mask includes,on the outside of the annular part (20), at least one arm (25) whichextends radially with respect to the annular part (20), in a cantileverfashion from the annular part.
 12. Process according to claim 7, whereinthe cross section of the annular part (20) is generally rectangular. 13.Process according to claim 12, comprising the further step of selectingthe mask to include, inside the annular part (20), at least onecrosspiece (24) which links together two regions of the annular part(20), the cross section of the crosspiece (24) being generallyrectangular, and the cross section of the crosspiece extendingapproximately parallel to the cross section of the annular part (20),wherein the cross section of the crosspiece and the cross section of theannular part are considered in the same cross section plane.
 14. Processaccording to claim 7, comprising the further step of selecting the maskto include, inside the annular part (20), at least one crosspiece (24)which links together two regions of the annular part (20).
 15. Processaccording to claim 14, wherein the crosspiece (24) extends along adiameter of the annular part (20).
 16. Process according to claim 14,wherein the mask includes at least two crosspieces (24).
 17. Processaccording to claim 16, wherein the two crosspieces (24) of the mask areperpendicular to each other.
 18. Process according to claim 14, whereinthe mask includes, on the outside of the annular part (20), at least onearm (25) which extends radially with respect to the annular part (20),in a cantilever fashion from the annular part, along an extension of onecrosspiece (24).
 19. Process according to claim 18, wherein the arm (25)and the crosspiece (24) have like cross-sections.
 20. Process accordingto claim 18, wherein the arm (25) is located at each of the ends of thecrosspiece (24).
 21. Process for the vacuum treatment of any curvedsubstrate having a circular contour with a given diameter (D₁),comprising the steps of: depositing a layer of material coming from agiven source of material (13) on the curved substrate (10), whileinterposing a mask (19) between the curved substrate (10) and the sourceof material (13) at a certain distance from the curved substrate (10),the mask being stationary with respect to the curved substrate (10), andselecting the mask to have an annular part (20) satisfying at least oneof the following formulae:d+H=A·D ₂/2  (I)d=B·D ₂/2  (II)D ₁ =C·D ₂  (III) in which: d is the distance between the mask (19) andthe highest point of the treated curved substrate (10); H is the heightof the annular part (20) of the mask (19); D₁ is the diameter of thecurved substrate (10); D₂ is the diameter of the annular part (20) ofthe mask (19); A is a coefficient of between 0.8 and 1; B is acoefficient of between 0.7 and 0.9; and C is a coefficient of between 2and
 3. 22. Process according to claim 21, wherein, A is about 0.92; B isabout 0.77; and C is about 2.5.